Automatic alignment system



April 4, 1961 Filed Aug. 2l, 1957 C. SHUMARD AUTOMATIC ALIGNMENT SYSTEM6 Sheets-Sheet 1 [HARLES E. SHUMARD April 4, 1961 c. c. sHuMARDAUTOMATIC ALIGNMENT SYSTEM 6 Sheets-Sheet 2 Filed Aug. 21, 195'?INVENTOR. [HARLES E. SHUMAKD 3%@ am,

April 4, 1961 c. c. SHUMARD 2,978,646

AUTOMATIC ALIGNMENT SYSTEM Filed Aug. 2l, 1957 6 Sheets-Sheet 3 ,mm 457/42M 44./ 412/ 42,1 41,2/ (Mc/Jia,

. I i l INVENTOR. [HARLES [.SHUMARD TTUENEY April 4, 1961 Filed Aug. 2l,1957 VIII"- April 4, 1961 c. c. SHUMARD 2,978,646

AUTOMATIC ALIGNME'NT SYSTEM Filed Aug. 2l, 1957 6 Sheets-Sheet 5 Il F.(9.

IN VEN TOR.

April 4, 1961 c. c. sHuMARD AUTOMATIC ALIGNMENT SYSTEM 6 Sheets-Sheet 6Filed Aug. 21, 1957 INVENTOR. [HARLES II. SHUMARD TTaRNfY United StatesPatent O AUTOMATIC ALIGNMENT SYSTEM `Charles C. Shumard, Hopewell, NJ.,assgnor to Radio Corporation of America, a corporation of Delaware FiledAug. 21, 1957, Ser. No. 679,421

4 Claims. (Cl. S30-2) The present invention relates to an alignmentsystem for automatically aligning electric circuits, and moreparticularly to an improved system which accurately and quickly tunesresonant circuits to a predetermined frequency.

In many instances, it is necessary to align an electrical circuit to apredetermined frequency. For example, each of the radio and televisionreceivers which are now being produced in great volume include a numberof resonant circuits which must be tuned to the correct operatingfrequencies. Up to the present time, the alignment of such resonantcircuits has been performed manually by trained operators. Each operatorviews the response kof each resonant circuit on an oscilloscope, or onan indicating meter, and manually tunes the resonant circuit to thecorrect frequency as indicated by a maximum or peak response of theresonant circuit. Such an alignment procedure is inherently laboriousand time consuming and requires skilled personnel to manipulate the testequipment and interpret the data obtained. While a human operator canalign a single resonant circuit with good accuracy and in a relativelyshort period of time, when he attempts to align resonant circuits oneafter the other, he is unable to operate with any acceptable speed oraccuracy over long periods of time. Consequently, when tunable circuitsare aligned manually, the results are unreliable and non-uniform.

Attempts have been made in the past to provide automaticV alignmentapparatus for tuning a single resonant circuit to a predeterminedresonant frequency, by bserving the peak response of thecircuit whenexcited by a signal of the predetermined frequency. However, Ythisprocedure is not satisfactory for applications such as multi-stagestagger-tuned amplifiers, wherein interstage coupling transformers aretuned to provide an overa-ll predetermined frequency responsecharacteristic for the amplifier. This is particularly true Voftelevision receiver picture LF. amplifiers wherein the frequencyresponse characteristic must be accurately controlled to preventundesired interaction between the sound and picture signals.Furthermore, it is impractical to peak align a single resonant circu-itat a time to a predetermined frequency since connections must be madedirectly to the individual circuits thereby introducing external effectssuch as loading and' lead capacitance, etc., which adversely affect thetuning of the individual circuits. It is, therefore, desirable to haveay fully automatic alignment system wherein the resonant circuits can beaccurately, reliably, and uniformly aligned to providethe correctfrequency response characteristic. Also, it is desirable to decrease thetime required to tune each circuitY Patented Apr. 4, 1961 vide a new andimproved apparatus for automatically aligning electric circuits topredetermined frequencies.

It is another object of the present invention to provide an improvedautomatic alignment system for tuning cascaded resonant circuits in amanner to provide a desired frequency response characteristic which issuitable for unskilled operators on a production line basis. Stillanother object of this invention is to provide an improved automaticalignment system wherein a plurality of cascadek resonant circuits maybe aligned to a desired frequency response characteristic withoutrequiring individual connections to each of the resonant circuits. It isa still further object of this invention to provide an improvedautomatic alignment apparatus for aligning to the correctvr frequencyresponsecharacteristic Without employing highly skilled technicians, sothatmore receivers can bey tuned ina given period of time and the lexpenseof operating personnel can be reduced; Y

Itis, according1y,yanfobject of this inventionto pmstagger-tunedelectric circuits to a predetermined frequency response characteristicwherein such alignment may be accomplished by unskilled operators in aminimum amount of time on a production line basis and with a high degreeof uniformity of the aligned circuits.

In accordance with the present invention the frequency response ofapparatus including a plurality of tunable circuits to be aligned issequentially measured at different selected signal frequencies. Theresponse of the apparat-us at each of the selected signal frequencies iscompared with standard or reference signals representative of thedesired output level at that frequency. Any difference between themeasured level and that of the standard is used to control a servosystem connected to automatically adjust the tuning elements of theresonant circuits. In this manner a stagger-tuned amplifier such as usedin radio or television receivers can be quickly and accurately adjustedto a predetermined frequency response characteristic.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof will best beunderstood from the following description when read in connection withthe accompanying drawings, in which:

Figure 1 is a schematic circuit diagram in block form ofV an automaticalignment system in accordance with the invention;

Figure 2 is a schematic circuit diagram of an intermediate frequency'amplifiery for television receivers which may be automatically alignedwith the system of the present invention;

Figure 3 is a graph of a desired frequency vs. amplitude characteristicfor the intermediate frequency amplifer shown in Figure 2;

Figures 4, 5 and .6 are detailed schematic circuit diagrams of portionsof the automatic alignment system shownin block form in Figure l;

Figure 7 is a schematic circuit diagram in block form vof'anotherembodiment of an automatic alignment system in accordance with theinvention; and' Figures 8, 9, l0 and l1 are detailed schematic circuitdiagrams of portions of the automatic alignment system shown in Figure7.

Referring now to the drawings and more particularly to Figure 1 thereof,there is illustrated Vin block diagram form one alignment systemembodying the present inrquencyamplifier which-is to be aligned toprovide a predetermined frequency` responseV characteristic. The LF,

amplifier of the receiver is indicated as having at least threeinterstage coupling transformers 12, 14 and 16 which are individuallytunable to a desired frequency of resonance by the movable tuning slugs18, and 22.

A sweep frequency generator 24, operable to provide a signal cyclicallyvarying in frequency over the band of frequencies to be passed by theLF. amplifier under alignment, is connected to the receiver 10 through aconducltor u. The sweep frequency signal from the generator 24 is alsoapplied through a conductor 25b to a prealigned reference receiver 26,and three tuners 28, and 32 each of which is tuned to a differentfrequency in the frequency band covered by the sweep frequency generator24. The reference receiver 26 is a prealigned receiver having apredetermined frequency response characteristic corresponding to apredetermined standard to which it is desired to adjust the receiver 10under alignment. Y

The output signals from the receivers 10 and 26 in response to theapplied signal from the sweep frequency generator 24 are compared in achopping circuit 33.

The chopper 33 has a pair of fixed contact terminals 34 and 36 which areconnected with respective receivers 10 and 26,7and a movable element 38which alternately makes contact with the terminals 34 and 36. Thechopping circuit 33 performs the function of converting the vdifferencein output signal levels between the receivers 10 and 26 into a squarewave of proportionate amplitude f and sense.

The square wave error signal from the chopping cir- -cuit 33 is Aappliedto each of three normally blocked servo vamplifiers 40, 42 and 44 by wayof a conductor 39. The servo amplifiers 40, 42 and 44 are connectedrespectively to drive the servo motors 46, 48 and 50 which in turncontrol the movement of the slug tuning elements 18, 2t) and 22.

In accordance with the invention, the alignment of the receiver 10 iscontrolled by measuring and comparing the response of the receiver ateach of a finite number of signal frequencies with that of the'referenceVreceiver 26. By way of example, three signal frequencies in the bandcovered by the sweep frequency generator 24 are arbitrarily selected formeasurement and comparison with the reference receiver 26. The threefrequencies selected for comparison, f1, f2 and f3 may be near the lowfrequency, center, and high frequency portions respectively of thereceiver pass band., It has been ascertained that the interactionof theeffects of tuning the transformers 12, 14 and 16 in the stagger-tunedinter- 'mediate `frequency amplifier is such that each may be tuned tocontrol different portions of the frequency response characteristicofthe amplifier. Accordingly, by

adjustment of the tuning slug 18 of the transformer 12,

the frequency response at the low frequency end of the -passband can bepredominantly controlled. Likewise, by

adjustment of the -tuning slug 20 of thetransformer 14, the highfrequency end' of the, passband can be controlled and the tuning slug 22of the transformer 16 can be used `to control the tilt of the resultingfrequencyvresponse characteristic. t s

As the sweep frequency generator 24 approaches the frequency f1 to whichthe tuner v28 is tuned, a control signal is developed by that tunerwhich serves as a gating pulse to unblock the servo amplifier 40. Thesignals at 4frequency f1 which are simultaneously fed to the refer-.ence receiver 26 and the receiver under alignment 10 are compared inthe chopper 33. .Any difference in th'e amplitude of the signal outputof the receivers 10 and 26 is amplified in the servo amplifier 40 todrivethe motor 46 which adjuststhe tuning slug 18.- This tunes thecoupling transformer 12 to change the frequency -response of thereceiver 10 at the frequency f1 to correvspond to that of the referencereceiver 26. k-As the' sweep v frequency generator `24 continues totunecyclically over .the band, vand approaches thefr'equency t whichrthetuner 30 is tuned, the output from the tuner 28 decreases and the servoamplifier 40 returns to its normally blocked condition. However, thesignal output from the tuner 30 operates to unblock the servo amplifier42 so that any error signal at the frequency f2 from the referencereceiver 26 and the receiver 10 is amplified to control' the motor 48.In turn, the motor 48 drives the tuning slug 20 to adjust the responseof the receiver 10 under alignment at frequency f2 to correspond to thatfrom the reference receiver 26. In like manner, the vtuner 3 2 producesa signal to actuate the servo amplifier 44 soI that the response of thereceiver 10 at frequency f3 may' be adjusted to correspond with that ofthe reference re' ceiver 26. The net effect of the foregoing operationsis to energize each of the three servo loops in sequence so that anyerror in the response of the receiver being aligned at the frequency f1is compensated by tuning of the transformer 12, and any error in thealignment at the frequency f2 is compensated by tuning the transformer14, etc.

The alignment process outlined above is repeated until the circuits ofthe receiver 10 are brought into precise alignment with the prealignedcircuits of the reference receiver 26.

The cyclically varying rate at which the sweep frequency generator 24covers the desired frequency range is slow enough for proper operationof the servo loop. It should be noted that fixed frequency sources maybe .used in the place of the sweep frequency generator 24,

*components briefly described above, the operation of these componentswill be analyzed insofar as possible in Aterms of the functions whichthey perform in tuning the resonant circuits 12, 14 and 16 to providesubstantially the same response characteristic as the reference receiver26. Before considering the details of the system components, however, itis pointed out generally that corresponding reference characters havebeen used throughout the drawings to identify corresponding cir- Ycuitelements of the system. Unless necessary to an 'understanding of theoperation of a particular system component, those circuit elements whichperform entirely conventional functions in the circuit, namely,functions which will be readily understood by those skilled in the art,have not been identified in the drawings nor referred to in thefollowing description of the system components.

Figure 2 schematically illustrates a portion of a television receiverincluding a conventional stagger-tuned Aamplifier circuit of the typewhich may be automatically aligned by means of the apparatusdescribedabove with reference to Figure l. In addition to theintermediate frequency amplifier, the schematic of Figure 2 shows theusual mixer stage 52 incorporated in superheterodyne receivers forconverting a selected signal modulated radio frequency carrier to acorresponding intermediate frequency si'g'nal. The LF. signaldevelope'din the mixer output circuit is conveyed 'through an overcoupled passivenetwork'54 to a staggertuned I.F.' amplifier including three amplifierstages 56, S8 and 60 "with tunable interstage coupling transformers 12,14 and 16. These transformers may be of any suitable type such as: woundon a suitable coil form` and tuned by` a centrally movable tuning slug;or printed on an insulating supporting panel and tuned by eddy currentdisks `/which'may be moved toward or away fromthe res'pective windings;lzffter, amplificationv byv the Aamplifici', the signal? is detected in"a rectifiercircuit Y62 'com nected' tothe. secondary windingof theAtransformer '16, which comprises the video detector stage of thetelevision receiver 10. f

The signal from the-swcep` frequency generator 24 is appliedy to .the-inputv terminal 64` which is` coupled to the control grid of thev mixerstage 52, and the amplified output signal from the LF. lamplifier isderived from a terminal 66 which is coupled to the anode of the videodetector. The conductors 25a and 31y Shown in Figure 1 are connectedrespectively to the terminals 64 and 66.

An example of a desired overall frequency response curve for thestagger-tuned amplifier is shown in Figure 3 and -represents a standardresponse for a television receiver I.F. amplifier.,` `In;.this\` curvethe frequency of an applied signali of substantially constant amplitudeis indicated along the 'abscissa and relative amplitude of the vsignalappearing at the output terminal 66 is indicated onv thel ordinate. Asshown on Vthis curve the pass band of the intermediate frequencyamplifier of Figure 2 lextends over a range of frequencies from about 41to 46 megacycles. `In aligning a stagger-tuned amplifierto provide thisfrequency response characteristic,

ytfis necessary to formalize the` effects of the transformers 12, 14and`16. This was found to befpossible by applying the followingcriterion: The transformer 12 affects `mainly thek \low frequencyportion of the response curve, and is .tuned to adjust the response 4ofthe amplifier fora signal input frequency of 41.6 megacycles; thetransformer 14 affects mainly the high frequency portion of the responsevcurve and is tuned to adjust the response for a signal input frequencyof about 45.75 megacycles; andthe transformer 16. affects the tiltl ofthe response curvevbetween the low and high frequency ends of the passband and is. adjusted in accordance .with thel response of theamplitierpfor a signal. input frequency of about 43.25 megacycles Aspreviously pointed out inthe general description Lof the system inFigure 1, the. tuners 28, 30` and 32 in the respective servor loopsperformv the function yof providing a gating pulse which unblocks theservo ampli-A fiers so that the error voltage output from the, choppingcircuit 33 may be used to drive one ofthe motors. The tuners are tunedto different frequencies so that only one servo loop is operable at -atime. By way of example the tuners 28, 30 and 32 are tunedy to 41.6,45.75 and 43.25 megacycles respectively thereby causing the response'ofthe amplifier under alignment to be sampled and compared at thesefrequencies. Since the construction of the three ytuners is similar onlythe tuner 28. has been illustrated.,

is connected through an isolating resistor 70 tothe input `Ycircuitofthe tuner. The input circuit includes a parallel v resonant circuit 72connected'between the control gn'd of a'highfrequency amplifier tube 74and ground which in the case of the tuner 28 is'designed to selectsignals at" 41.6 megacycles applied to the inputc'ircuit thereof.

The parallel resonant circuit 72 need notbe sharply tuned tov the centerfrequency thereby permitting a -relatively wide gating pulse. The outputcircuit for the R.F.

amplifier comprises a parallel resonant circuit,76 which includes theprimary winding of a'ecoupling transformer gating voltage of the. properpolarity to overcome the blocking bias applied to the servo amplifier.40.,

In considering the operation ofv the ,tuner shown 1n `'Figure 4, as thesweepfrequency generator 24 approaches the, frequency towhich aparticular tuner `is responsive, a`

signalvoltage isv developed .at the control grid of the f 1 f "5o t Theconductor 25b from sweep frequency generator 2.4

quencyygeneratorcontinues to ohangein frequency, the amplitude ofthegating; pulse gradually decreases to zero.

The circuit shown in detail in Figure 5 of the drawings, and,.asdiscussed briefly in the general system of Figure l-, is provided forthe purpose of converting the gradually varying output voltage fromA theLF. amplifier under alignment into a square waveof correspondingamplitude and sense which may be amplified in A C. coupled amplifiers tocontrol the driving motors 46, 48 and 50. The chopping -circuit 33comprises a vibratory element or armature 38 whichl is polarizedso as tobe movedback and forth between the fixed contacts 34 and 36 dueto theattraction and repulsion of the magnetic fields set up by anadjacentarmature coil-84. The coil 84;,is excited with a sinusoidal voltage fromav standard frequency voltage source, not shown, so thatthearmature 38is moved back and forth at a rate corresponding to thefrequency of thesource. The fixedV contact 34 is. connected via a` conductor 31 to theoutput terminal of the receiver 1 0 ,whereas the fixed contact terminal36 is connected with samer potential, a square wave of voltage isproduced on the output conductor 39- of the chopping circuit 33 having afrequency corresponding to the frequency exciting the armature coil 84.As the receiver 10 is brought into align ment with the referencereceiver 26, the potential existing on the terminal 34 approaches andbecomesy equal to that on the terminal 36 and therefore no variation inpotential exists on the conductor 39 of the chopping circuit as thearmature 38 moves back and forth between the contacts 34 and 36. Thusthere is no output signaLfor amplification by the servo amplifiers todrive the motors.

Referring now to Figure 6 of the drawings a conventional A.C. amplifieris illustrated which is designed to amplify the square wave error signalproduced by the chopping circuit 33. The servo amplifier illustratedcorresponds to any of the amplifiers 40, 42 or 44 shownin Figure l. Thesquare wave which is provided at the armature 38 of the chopping circuit33 is applied by way of the conductor 39 and the coupling condenser-86to the control gridof a firstL amplifier stage 90. A second amplifierstage 92 which is A.C. coupled to the first stage drives a phasesplitter stage 94. In turn the phase splitter 94 provides a pair of 180out-of-phase signals to a puslrpull amplifier 96., The first aud secondA.C. amplifier stages 970 and 92 are normally biased toa nonconductiugcondi-tion by a negative voltage applied to the control grids thereof.As indicated, this negative voltage is provided by a battery 98, thepositive terminal of which is grounded with the negativey terminal beingconnected through suitable current limiting resistors to the controlgrids of the A.C. amplifier stages 90 and 92. The output from the tuner28 to which theservoampliiier 40 is connected is also appliedto thecontrol grids ofthe A.C. amplifiers -90 and 92 throughanisolatingresisftor 100. When the' tuner 28 produces a gating pulseV of"sufficient amplitudethe potential at; the. control grids of vtheamplifiers 90 and 92is yraised above cut-off` so that the ...amplifier74 willich is amplified and detected byr rthe rectifier 8i). The;detectedr signal voltage:y is filteredtoproi f f vide agatingp ulse for'theservo` amplifier tor whichthe windingl of the servo motor46,isfeonneeted tothe secondarywinding of the push-pull amplifierg96.`Thus the motor 46 isv driven in accordance with the 1magnitude andsense of the square wave input ltothe servo amplifier 40'. T ieotherservo amlpifiers 42l and 44areconnectfedinlike tuner is connected.signa1 .frointhe j sweep fre-75 manner.

Another embodiment of the automatic' alignment system of the inventionis shown in Figure 7. This-system is generally similar to that shown anddescribed in connection with Figure 1 except that means are providedwhereby the relative output signals from the receiver under alignmentand the reference receiver 126 are stored so that the tuning motors maybe continuously energized to drive the respective ltuning slugs. K Y

In this regard the sweep -frequency generator 124 applies a signalcyclically va-rying in frequency to the receiver 10 under alignmentandthe pre-aligned receiver 126.

When the apparatus under alignment is an LF.A amplitier for televisionreceivers as shown in Figure 2 and the desired frequency responsetherefor is shown in Figure 3, the generator 124 may be set to deliver asweep'signal which cyclically varies over the frequency range from 40 to48 megacycles at a rate of 60 cycles per second. The signal from thegenerator 124 is also fed to each of three tuners 128, 130 and 132 eachof which, as described above in connection with Figure 1, are in adifferent servo loop for tuning the transformers 12, 14 and 16. Each ofthe servo loops also includes a triggering circuit 134, y136 and 138 anda pair of memory circuits 140 and 142, 144 and 146, 148 and 150. One ofthe memory circuits in each of the servo loops is connected to theoutput circuit of the receiver 10, and the other is connected to theoutput circuit of the reference receiver 126. The memory circuits do notaccept informaiton supplied by the respective receivers except whentriggered by the triggering circuit connected therewith.

Each of the rservoloops is also provided with a chopping circuit 152,154 and 156. The chopping circuits include la pair of stationary contactterminals, one connected to each of the memory circuits in therespective servo loop, and a vibratory armature element. The vibratoryarmature element alternately engages the stationary contact terminals toproduce a square wave of an amplitude corresponding to the difference inoutput between the receivers 10 and 26 and of a frequency correspondingto the rate of vibration of the armature. This square Wave is fed to aservo amplifier 158, 160 and 162, one for each `servo loop foramplification to control the driving motor's 164, 166 and 168. Since theinformation from the memory circuits is continuously available to thechopping circuits, an error signal is available to provide-continuouscontrol of the motors until the receiver 10 is in alignment with the.reference receiver 26.

A tachometer generator 1,70, 172 and 174 is coupled to each of the servomotors 164, 166- and 168 respectively.

PThe tachometer output signal is summed together with the amplifiedchopper signal.k Thus the overall servo loop including the receiver 10is a' positon servo while a velocity servo loop is obtained with theservo motor and amplifier. The vamount of tachometer feedback used ineach loop may be determined experimentally, and is adjusted to result ina fast and stable system.

In the quantity manufacture of electronic equipment such` as receivers,the amplifier portions thereof under alignment do not always have thesame gain. Accordingly, it is desirable that the frequency responsecharacter- -istic be adjusted relative to the reference receiver rather'than adjusted to an absolute level. To this end, an AGC circuit 175 isprovided which develops a gain control potential as a function of theoutput level of the receiver 10. The AGC voltage isv applied to thepre-aligned receiver 126 to produce .any overall characteristic curve ofgenerally the same area `as that of the devioe'under adjustiinentl f f'fvIn considering the detailed circuitryV of the automatic alignmentsystem shown `in Figures 8 tov ll and brieyA described above, theoperation of these components Will be analyzed in termsof the functionswhich theyperform intuning the resonant circuits 12, 14 and 16 toprovide,

substantiallythe same frequency response cllaracter'istic` as thereference receiver 126.

Since the three servoloops are substantially identical except for thefrequency at which the tuners produce a triggering pulse, only one ofthe servo loops will vbe described in detail. As pointed out above, eachof the servo loops controls one of the motors 164, 166 and 168 whichtunes the transformers 12, 14 and A16 respectively.-The tuning of thetransformer 12 predominately controlsv the low frequency'response of theamplifier being aligned, the transformer 14 predominately controls thehigh frequency response of the amplifier being aligned, and thetransformer 16 predominately controls the slope of the resultingfrequency response characteristic curve. Accordingly, the tuners aretuned to different frequencies so that the memory circuits in only oneof the servo loops at a time is operable to receive information from thereceivers`10- and 126. By way of example, the tuners 128, 130 and 132are operable to produce triggering pulses when the frequency of thesweep generator is at 43, 45.5 and 44.5 megacycles respectively, therebycausing the response of the amplifier under alignment to be sampled andcompared at these frequencies.

The tuners 128, 130 and 1-32'of the automatic alignment system of Figure7 is shown in Figure 8. Basically, the operation of this circuit is asfollows: the signal output from the sweep generator 124 is mixed with asignal from a self contained Vlocal oscillator tuned to the desiredsampling frequency. The mixer output is fed through a low pass filterwhich transmits they zero beat of the difference frequency. Theresulting burst, peaked at the beat frequency, is amplified, rectified,and integrated to form a positive pulse.v This pulse is used to triggera univibrator` (triggering circuits 134, 136 and 138.) which in turnprovide gate pulses to operate the memory circuits. .l

Referring to` the tuner 128, `a cathode'follower stage 178 whichprovides isolation from the other servo loops injects the sweep signalfrom the generator 124 at the cathode of a self oscillating converterstage 176. The frequency of the oscillator portion of the converterstage 176 is controlled by a crystal 180 at 43 megacycles for the tuner128. For the tuners 130 and 132 the4 oscillator frequency should be 45.5and 44.5 megacycles respectively. v Of the many resultant frequencycomponents present in the plate current of the converter 176 only aportion of the difference frequency containing the zero beat will appearacross the plate load resistor beat can be of varying positive ornegative amplitude' depending upon the relative phase of the two mixedsignals. This leads to an envelope whose desired positive half has anirregular peak amplitude. Accordingly, this signal is fed through a halfwaverdoubler 186 including the rectiiiers 188 and 190, so thateach'negative half cycle is added to each succeeding positive halfcycle.

YThe resulting transformed envelope is detected by an output capacitor192, and is used to key the triggering circuit 134. v

The triggering circuit134 as shown in Figure 9 comprises a cathodecoupled vunivibrator 194. To avoidmultiple triggering on an input pulsethe delay of a univibrator is made appreciably longer than the triggerpulse from the tuner 128. The level at which the univibrator 194 may betriggered can be varied by altering the grid Abias on the Vinput stage.

The output from the univibrator v194 is differentiated to provide asharp'trigger pulserfor agating univibrator 196. TheV time delay. of thegating univibrator 196 is .adjusted to giveV a gate width of sufficientduration to permitrproper operation of the vmemory circuits N and 142.Gating pulses of opposite polarity are availf able from/thev anodecircuitsof the tubes198kaud 2400 respectively ofthe'univibrator196.

' age to the tuning controls.

t The opposite polarity pulses from the gating univibrator yi196 areapplied to the memory circuits 140 and 142.

i' Since the two memory circuits 140 and'142 are identical .only the`memory circuit 1'40 has been illustrated in Figure 10. The voltage to`be sampled which in thecase of the memory circuit 140 is the outputlsignal from the receiver 10, and in the case of the memory circuit 142is the output signal from the pre-aligned receiver 126 is applied to thememory circuit input terminal l202. The resultant information appearingat the input terminal 202 is stored in a memory capacitor 204 when thememory circuit is triggered by a-gating pulse from the gatingunivibrator 196. The memory circuit includes four diodes 206, 208, 210kand 212. In the quiescent state, two bias voltages, one ra negativevoltage applied to the cathode of the diode 206 and the other a positivevoltage applied to the anode of the diode 210 causes these diodes .toconduct.` The current through the diodes 206 and 210 cause a voltage tobe developed across the resistors 214 and 21'6 whichfis of a polarity tomaiutain the diodes 20.8 and 212 knon-conducting. When positive andnegative pulses vare applied respectively to the terminals 221 and-220from the gating univibrator 196, the diodes 206 and 210 are cut-O, andthe linput voltage from the receiver under alignment y can charge VinlFigure 3- ofthe drawings.

' The'anodes 'of-the respective tubes in the push-pull outtputfstage228:are connected respectively to Athe field yvindingrof the motor 164, tocontrol the position of the motor armature in accordance with the errorsignal applied to the servo. amplifier 158.

In the operationof the automatic alignment system shown land describedin connection with Figures 7 to 11, the apparatus to beY aligned isfirst placed in an alignmentxture, and the tuning elements of the tubetransformers 12,Y 14 and 16 are mechanically coupled to the respectiveservo motors 164, 166 and 168. In the first step of the aligningprocedure, the three transformers are detuned mechanically by adjustingthe tuning slugs to a limit by either providing a predetermined inputsignal through thesystem or by mechanically detuning prior to theinsertion of the tuner into thealignment rack. In the second stage allof the servo loops are energized, and the servos will position theVtuning ad- 'justments to4 result in'an alignment response curve shownThe alignment system 'of the presentl invention is capable of accuratelypositioning the three .tuning slugs in about three seconds.`Specifically `the output signals from the receiver under -aligrimentandthe pre-aligned receiver 126 are each conthe memory capacitor 2,04through the diodes 208 or 212 depending upon the polarity ofthe inputsignal. For optimum operation, the contact potential of the diodes 208and`212 'should be equal. However, good results may be obtained in thisrespect by reducing the filament voltage of the diodes below the ratedvalue. Under these conditions it is fairly simple to select diode tubesland to obtain output voltages equal to the input voltage to about plueor 'minus .01 volt. time constant of the circuit including the memorycapacitor 204 is longer than the gating interval so that several cyclesare required to bring the capacitor up to full charge. This however, isof no disadvantageV asthe time constant of the servo loop ismuchfgreater than the time constant of the sampling circuit. Y

The voltage across the memory capacitor 204-is available 'at an outputyterminal 218 for application 'to the chopping circuit 1,52fwhic`h is`-shown in Figure 11. In

The charging jtinuously appliedV to the input terminals of a differentIrneir'iory'circuitin each of the three servo loops. As

vlthefsweep*frequency generator 124 approaches the frequencyY fi(approximately 43 megacycles) to which the tuner 128 is tuned, a pulseis produced which keys the triggering circuit 134. The triggeringcircuit in turn "gates the memory circuits 140 and 142 for apredetermined' time period to receive information from the receiver'l()under alignment and the pre-aligned receiver 1,26 respectively. Thisinformation is stored as a charge on a memory capacitor provided in eachof the memory circuits', and is applied kto the fixed terminals of ,thechopping circuit 152. When the output level ofthe receiver "underalignment differs from the signal output from the i pre-alignedreceiver126 the charge on the memory capaclike manner, the charge across thememory capacitor..

for the memory circuit` 142 which stores the reference receiver 1,26information ris available at any output terminal 223'for application tothe chopping circuit. The vibratory armature element of the chopper isconnected yto the input circuit of theservo amplifier 158,. g

Theerror signal applied tok the Iservo amplifier V158 is amplified by apentode amplifier 2,19 and coupled to a cathode follower stage 222.`The. signal coupling circuit between the cathode follower stage 222-andan amplifier stage 224 in the servo amplifier 1'5f8`includes avlimitswitch 225. In the normagloperation `of thesystem the limit switchcompletes. the circuit between the cathode follower 222 and theinput`circuit forfthe amplifier stage 224. Eachservo motor lhas an oifsetfonthe shafty that will operate the krlimit'switches associated with theparticular motor at either endof the` normal tuning range of the tuningelements in the transformers 12, 14

and 16. At either limit the switch 225 is actuated to ground the outputof a cathodefollower stageso that no error signal may be developed todrive the ytuning motor 164. This provides a safeguard to prevent dam-The output signal from the tachometer generator is also coupled to theinput circuit of the amplifier stage 224. The tachometer output signalissummed together 'with the amplified chopper signal. The amount oftachometer'signal used in each loop varies and may be. determinedexperimentallyfor The amplifier stage 224 is coupled vto a phaseysplitter 226 which drives a push-pull output amplifier stage 228.

itors in the memory circuits 140 and 142 will be different. Accord'nglyan error voltage will be developed by thechoppin'gfcircuit 152 which isamplified in the servo amplifier 158 to drive the motor 164. The motor164 `tunes the coupling transformer 12 to adjust the response ofthereceiver under alignment in the direction of the predeterminedY responseestablished by the pre-aligned `As'the'sweep frequency generatorcyclically continue overthe frequency range and approaches the frequencyj136. Inthe meantime the gating pulse from the triggering circuit 134 tothe memories 140 and 4142 has `expired so that information from thereceivers no-longer affects these circuits. However, the triggeringcircuit 136 produces gating pulses to condition the memory cir-'cuits`144 and 146 to receive information from the receiver K bestoperation to provide' fastr and` stable servo loops.y

underalignment andthe Apre-aligned receiver 12S-in responseato 'the'44.5 megacycle input-to thesey receivers.

Any difference in the response of these receivers is utilized to producean error signal by means of the chopping circuit 154, which error signalis amplified by the servo amplifier 160 to drive the servo motor 166.This predominantly corrects the high frequency response of the receiverunder alignment. f

In like manner the tuner 132 when energized by a sweep frequencygenerator signal corresponding to the frequency f3 (43.5 megacycles)lenergizes the third servo loopto Vtune the transformer 16 and correctthe relative response between the high and 10W frequency ends of thereceiver passband.V Itshould be understood that lthe entire f operationof this cycle is completed in a very short time,

and standard sweep frequency generators having a 60 cycle 'y n persecond sweep rate have been successfullyused.

Since it is probable that the gain of the receive'rrunder l1 alignmentmay not correspond exactly wth'the gain' of the reference receiver 126,an automatic gain control potential which is derived as a function ofthe output signal level of the receiver is applied to control the gainof the pre-aligned receiver 126. For example, if the rey ceiver 10 has agreater gain than normal, the pre-aligned receiver 126 gain is adjustedby means of the AGC circuit to produce a larger output so that theadjustment of the frequency response characteristic is dynamicallycontrolled and conforms to a relative rather than a fixed standard.

The automatic alignment system of this invention quickly and accuratelyoperates to align tuned circuits such as stagger tuned amplifiers to apredetermined frequency response characteristic by comparing theresponse of the receiver under alignment with a standard such as areference receiver.

What is claimed is:

1. An automatic alignment system for aligning a tuned amplifier having aplurality of tunable circuits to a predetermined response characteristicover a desired frequency passband comprising, a sweep frequencygenerator operable to produce a signal cyclically varying in frequencyover at least a portion of said passband,

a reference amplifier pre-aligned to a predeterminedY frequencyresponse, means applying the signalV output from said sweep frequencygenerator to said tuned amplier and said reference amplifier, a choppingcircuit connected to said tuned amplifier and said reference amplifierfor comparing the response of said amplifiers to sig-vY nals from saidsweep frequency generator and oper-.

' to-unblock said pair of memory circuits to store signal informationrepresentative of the response of said ampli- 'fiers to signalsfrom saidsweep frequency generator, the

erator torunblock the memory circuits connected therewith.

3. VAn automatic alignment system for aligning a plut`rality of tunableamplifier circuits connected in cascade relation to a predeterminedfrequency response characteristics comprising, means for' sequentiallyenergizing said circuits at different predetermined frequencies in thefrequency range to be passed by said circuits, tuning means forindividually varying the .tuning of each of said tunable amplifiercircuits, means providing reference signals representative of thedesired response of said cascade tunable circuits at said differentpredetermined frequencies, means comparing the response of said cascadetunable circuits at each of said different predetermined frequencieswith the corresponding reference signal for .said frequencies to deriveerror signals, and servo control means responsive to said error Asignalsfor adjusting said tuning means.

4. An automatic alignment system for aligning a stags ger-tunedamplifier having a plurality of tunable circuits,

1 means for sequentially energizing said amplifier at difable to producean error signal representative of the mist tuning of said tunedamplifier, a plurality of normally inoperative servo-circuits includingya motor each connected to adjust the tuning of one of said tunablecir-i cuits in response to the error signal from said chopping circuit,and means for activating said servo circuits each at a different signalfrequency, said different signal frevquencies being provided by saidsweep frequency generator. Y

2. An automatic alignment system for aligning a stagger-tuned amplifierhavingV a plurality of tunable circuits to a predetermined responsecharacteristic over aY desired frequency passband comprising, a sweepfrequency generator operable to produce a signal ,cyclically varying: infrequency over at least al portion of saidv passband a referenceamplifier pre-aligned to a predetermined frequency response, meansapplying the signal Ioutput from "said sweep frequency generator to saidtuned amplifier andsaid reference amplifier, a plurality of servocircuitsfy feach connected to adjust the tuning of one of said tun;-

able circuits, each of said servo circuits including a chopping circuitfor comparing the response of said tuned" amplifier to signals from saidreferenceV amplifier,leach of said servo 'circuits including a pair ofvmemory circuits: Y connected to said chopping circuit, said memorycircuits having normally blocked input circuits connected respecv tivelywith said tuned amplifier and said referenceamplifier, each servocircuit including gating means connected 45t tuning means.

ferent signal frequencies in the desired amplifier passband, tuningmeans for individually varying the tuning of each of said tunablecircuits, means providing a plurality of reference potentials eachrespresentative of the desired x response of said amplifier at saiddifferent predetermined signal frequencies, means comparing the responseof said amplifier at a first of said different predetermined signalfrequencies with the reference potential corresponding to the desiredresponse of said amplifier at said first signal frequency to derive afirst error signal, servo control means responsive to said first er-rorsignal for adjusting one of said tuning means, means comparing theresponse of said amplifier at a second of said different predeterminedsignal frequencies with the reference potential cor- ;responding to thedesired response of said `amplifier at said second signal `frequency toderive a second error signal, and servo control circuit means responsiveto said second error signal for adjusting another of said ReferencesCited in the file of this patent UNITED STATES PATENTS 2,251,064

Martin et al V July 29, 1941 2,252,058 Bon Aug. 12, 1941 2,376,667Cunningham et al. May 22, 1945 2,465,531 Green c Mar. 29,1949

`2,634,373 Shostak Apr. 7, 1953 '2,719,270 Ketchledge 5. Sept. 27, 1955'2,727,994 Enslein Dec. 20, 1955 l2,753,526 Ketchiaigev s July 3, 19562,766,384 Prewitt v.. Oct.'9, 1956 Ashley .v K. July 15, 1958

